This invention relates to an apparatus for melting snow at the maximum rate and efficiency. More particularly, the present invention relates to a snow melting system including a sparger tube type submerged combustion apparatus.
Submerged combustion is a method of heating whereby hot products of combustion are forced through a medium to heat the medium. The heat exchange occurs directly between the hot products of combustion and the medium, which may be water or an aqueous solution. In a submerged combustion system, the hot combustion products are generated by a flame fed by a combination of air and a suitable fuel. The flame typically does not actually come into contact with the medium. This technology differs from conventional heat exchange methods such as immersion tube heating where the heat exchange is indirect from combustion products to the tube and through the tube walls to the medium. In conventional heat exchange methods, the spent products of combustion are inefficiently exhausted directly to the atmosphere with useable heat remaining, rather than being efficiently exhausted through the medium and giving up all possible heat, as is possible in submerged combustion.
A problem which exists in high latitude regions is melting large quantities of snow which must be cleared in, e.g., a city or an airport in winter. A variety of apparatuses and methods have been proposed for melting large quantities of snow. Generally these apparatuses and methods include various means for heating water and transferring the water""s heat to the snow. However, none of these methods efficiently combine high rates of heat transfer from the fuel to the water and from the water to the snow, as needed to achieve the maximum melt rate and fuel efficiency for melting snow.
Submerged combustion devices have been applied to the problem of heating water, both for production of hot water per se and for other applications such as melting snow. The submerged combustion devices used in prior art systems often employ a vertical combustor/weir style apparatus having a relatively small coverage area compared to the volume of water to be heated, in which the combustion gases are directed downwardly onto the liquid to be heated.
A weir type submerged combustion device includes two concentric vertical tubes of relatively short length. The tubes are vertically displaced, with the top and bottom of the outer tube (the weir tube) being lower than the respective top and bottom of the inner tube (the combustion tube). This tube system is vertically mounted and is partially immersed in the medium; usually about half the vertical length of the tubes are immersed. The bottom of the outer tube is located above the bottom of the medium container. In operation, the combustion products (hot gases) are directed downward against the surface of the medium in the inner tube. The hot gases are forced to pass downwardly through the medium, around the lower edge of the inner tube and up through the medium in the space between the inner tube and the outer tube. The hot gases entrain the medium and force it to rise in the space between the inner and outer tubes and then over the upper edge of the outer tube. At this point, the partially cooled gases escape upward and out of the device, while the entrained, warmed water flows downward on the outside of the outer tube and into the medium container thus mixing with the remainder of the medium. The only agitation of the medium is that provided by the water flowing into the bottom of the weir and out over the top edge of the outer tube.
The weir type of submerged combustion apparatus, while being currently used and thus the state of the art in snow melting, has shortcomings, in that it fails to completely transfer heat from the combustion gases into the liquid to be heated. The weir type of submerged combustion fails to achieve complete agitation of the container, and thus does not provide sufficient agitation of the snow melting water to rapidly melt the snow deposited in the snow melting apparatus. In addition, the lack of complete agitation results in non-uniform temperature distribution in the snow melting medium. Additional agitation must be provided from an external mixing device. Without adequate agitation, a problem arises due to accumulation of large masses of unmelted snow accumulated in the medium. The weir type of submerged combustion is inefficient in converting combustion heat to snow melting because the close contact of the flame with the water forms water vapor in the combustion chamber. These effects combine to limit the snow feed rate into the snow melting apparatus to less than what could be fed with full agitation and complete and uniform heat transfer.
In an attempt to overcome the problem of masses of unmelted snow resulting from the lack of agitation, users have increased the number of burners in a single snow melting tank. However, this solution merely shifts the location of the unmelted mass and, since each combustion unit provides only local agitation, does not solve the problem of inadequate agitation in the medium container as a whole. In addition, there are the additional capital and operating costs for the additional burners.
Thus, the needed agitation of the snow melting medium (e.g., water) has been left to the often inadequate passive mixing resulting from the water flow through the weir or has been provided by an external mixing device. The lack of agitation directly results in a reduced rate of snow melting and a loss in efficiency of fuel use as well. Other prior art systems include externally applied mechanical mixing devices, thus requiring the input of additional energy as well as provision of the additional equipment.
Due to these problems, snow melting has not been widely used. Instead, simple snow removal is often relied upon despite shortages of available disposal space and high transportation costs associated with snow removal.
An additional problem in the prior art has been the accumulation and concomitant requirement for removal of debris from snow melting operations. Accumulation of such debris is particularly problematical due to the wide variation in size and type of debris. For example, such debris may include sand, gravel, stones, glass shards and whole containers, wood, plastics of many shapes and sizes and various metallic objects which are inadvertently collected along with the snow. In prior art snow melting systems, the entire system must be shut down and the water drained out of the snow melting tank in order to gain access to and remove the debris collected with the snow. The problem is worse in cities than in controlled areas such as airports, but it is a general problem existing in snow melting operations. This requirement disrupts operations and wastes energy.
Therefore, a need remains for an apparatus and method which will rapidly and efficiently melt snow and provide for an efficient, continuous debris removal apparatus in association with the snow melting.
In one embodiment, the present invention relates to a snow melting apparatus including a container for holding a snow melting medium and receiving the snow; a submerged combustion burner; and a continuous debris removal mechanism.
In another embodiment, the present invention relates to a snow melting apparatus including a container for holding a snow melting medium and receiving the snow; a burner having a combustion chamber, wherein the combustion chamber comprises a sparger tube through which combustion gases emerge into, mix with and agitate the snow melting medium; and a continuous debris removal mechanism.
In one embodiment, the present invention relates to a snow melting apparatus comprising a container for holding a snow melting medium and receiving the snow; and a burner having a combustion chamber, wherein at least a portion of the combustion chamber is submerged in the snow melting medium and the submerged portion of the combustion chamber comprises a sparger tube through which combustion gases emerge into, mix with and agitate the snow melting medium. In one embodiment, substantially all of the combustion gases emerge into the snow melting medium.
In another embodiment, the present invention relates to a method of melting snow including steps of providing snow to a snow-melting apparatus, the snow-melting apparatus including a container, a submerged combustion burner and a continuous debris removal mechanism; operating the submerged combustion heating system to heat a snow melting medium which receives and melts the snow in the container; and continuously removing debris from the snow melting apparatus by means of the continuous debris removal mechanism. In one embodiment, the submerged combustion heating system includes a sparger tube.
In another embodiment, the present invention relates to a method of melting snow, comprising providing snow to a snow-melting apparatus, wherein the snow melting apparatus comprises a container for holding snow melting medium and receiving snow and a burner having a combustion chamber, wherein at least a portion of the combustion chamber is submerged in the snow melting medium and the submerged portion of the combustion chamber comprises a sparger tube; combusting fuel in the combustion chamber to form hot combustion gases; heating and agitating the snow melting medium by directly contacting the snow melting medium with the hot combustion gases exiting the sparger tube; and bringing the snow into contact with the heated snow melting medium to melt the snow.
Thus, the present invention relates to a snow melting apparatus in which water is the medium and which provides a high melt rate and high fuel efficiency. These benefits are attained by use of sparger tube submerged combustion, in which large volumes of hot combustion gases are brought rapidly, directly and intimately into contact with the snow melting medium. The hot combustion gases thereby both agitate a large portion or all of the snow melting medium and obtain nucleate boiling to most efficiently transfer heat from the hot combustion gases to the snow melting medium. Nucleate boiling provides much greater heat transfer from the hot combustion gases to the snow melting medium than does conduction or convection heating.
The present invention further relates to a snow melting apparatus including a mechanism for removing debris from the snow melting tank. In one embodiment, the snow melting apparatus includes a mechanism for continuously removing debris from the snow melting apparatus. In one embodiment, the mechanism for continuously removing debris from the snow melting apparatus includes a plate and flight conveyor, and in another embodiment, the mechanism for continuously removing debris from the snow melting apparatus includes a drag chain.